Method of transmitting control information in coordinated multi-point (COMP) system by a base station and receiving downlink data via a best downlink channel cell by a mobile station

ABSTRACT

A method of transmitting control information in a wireless communication system is disclosed. A method of receiving control information in a mobile station which receives downlink data from a plurality of cells simultaneously in a wireless communication system comprises receiving downlink control information including the control information on data transmitted from the plurality of cells from a serving base station via a downlink control channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. national stage application ofInternational Application No. PCT/KR2009/007143, filed on Dec. 2, 2009,which claims priority to Korean Application No. 10-2009-0115738, filedon Nov. 27, 2009, and U.S. Provisional Application Ser. No. 61/120,026,filed on Dec. 4, 2008, the contents of which are incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of transmitting control information in awireless communication system.

BACKGROUND ART

Generally, MIMO (multi-input multi-output) technique means a method ofimproving transceived data efficiency by adopting multiple transmittingantennas and/or multiple receiving antennas instead of a singletransmitting antenna and a single receiving antenna. Namely, the MIMOtechnique is the technique for a transmitting or receiving side of awireless communication system to attempt capacity increase orperformance enhancement using the multiple antennas.

The MIMO technique is the technique for receiving one whole message in amanner that pieces of data segments received via plural antennas are puttogether to complete the whole message. The MIMO antenna improves a datatransmission rate within a specific range or extends a system range fora specific data transmission rate, thereby being widely applicable to amobile communication terminal, a relay and the like. Many attentions arepaid to the MIMO technique as a next generation technology capable ofovercoming the transmission size limit of the mobile communication whichalmost reaches a dead end due to data communication expansion and thelike.

FIG. 1 is a diagram for a configuration of an MIMO communication systemaccording to a related art. Referring to FIG. 1, if the number oftransmitting antennas is incremented into N_(T) and the number ofreceiving antennas is simultaneously incremented into N_(R), theoreticalchannel transmission capacity is increased in proportion to the numberof antennas unlike the case that a transmitter or receiver uses aplurality of antennas. Hence, a transmission rate is enhanced andfrequency efficiency can be remarkably raised. The transmission rateaccording to the increase of the channel transmission capacity can betheoretically raised in a manner that a maximum transmission rate R₀ ofthe case of using a single antenna by a rate increasing rate R_(i) ofFormula 1.R _(i)=min(N _(T) ,N _(R))  [Formula 1]

For instance, an MIMO communication system, which uses 4 transmittingantennas and 4 receiving antennas, is able to obtain a transmission rate4 times higher than that of a single antenna system. After thistheoretical capacity increase of the MIMO system has been proved in themiddle of 90's, many efforts are ongoing to be made to varioustechniques to drive it into substantial data rate improvement. Some oftheses techniques are already adopted as standards for the 3G mobilecommunications and various wireless communications such as a nextgeneration wireless LAN and the like.

The trends for the MIMO relevant studies are explained as follows. Firstof all, many efforts are ongoing to be made in various aspects todevelop and research information theory study relevant to MIMOcommunication capacity calculations and the like in various channelconfigurations and multiple access environments, radio channelmeasurement and model derivation study for MIMO systems, spatiotemporalsignal processing technique study for transmission reliabilityenhancement and transmission rate improvement and the like.

In order to explain a communicating method in an MIMO system in detail,mathematical modeling can be represented as follows.

First of all, a transmission signal is explained. If there are N_(T)transmitting antennas, N_(T) maximum transmittable informations exist.Hence, it can be represented by the vector shown in Formula 2.s=└s ₁ ,s ₂ , . . . , s _(N) _(T) ┘^(T)  [Formula 2]

Meanwhile, transmission power can be set different for each transmissioninformation. If the respective transmission powers are set to

P₁, P₂, . . . , P_(N) _(T) ,

the transmission power adjusted transmission information can berepresented by Formula 3.ŝ=[ŝ ₁ ,ŝ ₂ , . . . , ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Formula 3]

And, the transmission power adjusted transmission information vector canbe represented by Formula 4 on a transmission power diagonal matrix P.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \lbrack {{Formula}\mspace{14mu} 4} \rbrack\end{matrix}$

If the transmission power adjusted transmission information vector ismultiplied by a weight matrix W, N_(T) transmission signals aregenerated. In this case, the weight matrix is the matrix that plays arole in properly distributing each transmission information to eachantenna according to a channel status and the like and is also called aprecoding matrix.

If the N_(T) transmission signals are set to

x₁, x₂, . . . , x_(N) _(T) ,

a transmission signal vector x can be represented by Formula 5. InFormula 5, w_(ij) indicates a weight between an i^(th) transmittingantenna and a j^(th) information.

$\begin{matrix}\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}}}} \\{= {{W\;\hat{s}} = {WPs}}}\end{matrix} & \lbrack {{Formula}\mspace{14mu} 5} \rbrack\end{matrix}$

In the following description, a reception signal is explained. WhenN_(R) receiving antennas exist, if reception signals of the receivingantennas are set to

y₁, y₂, . . . , y_(N) _(R) ,

a reception signal vector can be represented by Formula 6.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Formula 6]

In a wireless communication system using MIMO antenna, a channel can berepresented by an index of a transmitting antenna and an index of areceiving antenna. A channel between a transmitting antenna j and areceiving antenna I can be represented by h_(ij). This channel can berepresented by a vector or matrix in a manner of tying channels betweena plurality of transmitting antennas and a plurality of receivingantennas together.

FIG. 2 is a diagram of channels between a receiving antenna i and N_(T)transmitting antennas, respectively.

Referring to FIG. 2, the channels between the receiving antenna i andN_(T) transmitting antennas can be represented by a vector expressed asFormula 7.h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Formula 7]

And, channels between N_(T) transmitting antennas and N_(R) relievingantennas can be expressed as the matrix shown in Formula 8.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \lbrack {{Formula}\mspace{14mu} 8} \rbrack\end{matrix}$

A transmission signal passes through a channel and then has AWGN(additive white Gaussian noise) added thereto. If so, a reception signalis the signal. If white noses added to receptions signals received byN_(R) receiving antennas are set to

n₁, n₂, . . . , n_(N) _(R) ,

respectively, a white noise vector can be represented by Formula 9.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Formula 9]

Hence, a reception signal vector can be expressed as Formula 10.

$\begin{matrix}\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} \\{\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} \\{= {{Hx} + n}}\end{matrix} & \lbrack {{Formula}\mspace{14mu} 10} \rbrack\end{matrix}$

An MIMO system can be categorized into a space multiplexing scheme and aspace diversity scheme according to a presence or non-presence of thesame data transmission.

The space multiplexing scheme means the scheme for transmitting data athigh speed by transmitting different data via a plurality oftransmitting antennas simultaneously without increasing a bandwidth. Thespace diversity scheme means the scheme for obtaining transmissiondiversity by transmitting the same data via a plurality of transmittingantennas. Space time channel coding is an example for the spacediversity scheme.

The MIMO technique can be also categorized into an open loop scheme anda closed loop scheme according to a presence or non-presence of feedbackof channel information to a transmitting side from a receiving side. Theopen loop scheme includes a space-time trellis code (STTC) scheme forobtaining a transmission diversity and coding gain using BLAST and spaceregion capable of extending an information size amounting to the numberof transmitting antennas in a manner that a transmitting side transmitsinformation in parallel and that a receiving side detects a signal usingZF (zero forcing) and MMSE (minimum mean square error) schemerepeatedly. And, the closed loop scheme includes a TxAA transmit antennaarray scheme or the like.

FIG. 3 is a conceptional diagram for CoMP (coordinated multi-point) ofan intra eNB and an inter eNB according to a related art.

Referring to FIG. 3, intra eNBs 310 and 320 and an inter eNB 330 existin a multi-cell environment. In LTE (long term evolution) system, anintra eNB is constructed with several cells or sectors. Generally,physically co-located cells are called intra cells and cells indifferent locations are called inter cells, respectively. A single cellMIMO user within a single cell communicates with one serving cell in onecell (sector). A multi-cell user located on a cell boundary is able tocommunicate with a plurality of serving base stations in a multi-cell(multi-sector).

A coordinated multi-point (CoMP) system (hereinafter abbreviated CoMPsystem) is the system to improve data transmission efficiency of a userlocated on a cell boundary by applying enhanced MIMO transmission in amulti-cell environment. If the CoMP system is applied, it is able toreduce inter-cell interference in the multi-cell environment. If theCoMP system is used, a mobile station can be provided with a supportfrom multi-cell base stations jointly. Moreover, each base station isable to enhance system performance by supporting at least one or moremobile stations MS1, MS2, . . . MSK simultaneously using the same radiofrequency resource. Namely, the base station is able to perform spacedivision multiple access (SDMA) method based on status information of achannel between the base station and the mobile station.

The CoMP scheme can be categorized into a joint processing schemethrough data sharing and a coordinated scheduling scheme/beamformingscheme.

In a CoMP system, a serving base station and at least one or morecoordinated base stations are connected to a scheduler via awired/wireless network. The scheduler is able to operate by receivingfeedback of channel information on a channel status between each mobilestation (MS1, MS2, . . . MSK) and the coordinated base station.

In a wireless communication system, a base station transmits downlinkcontrol information to a mobile station. The mobile station transmitsuplink control information to the base station. Therefore, the demandfor a method of transmitting control information in a CoMP system isongoing to rise.

DISCLOSURE OF INVENTION Technical Problem

However, as mentioned in the foregoing description, as a CoMP system isintroduced, the demand for a method of transmitting control informationin a CoMP system rises.

Accordingly, the present invention is directed to a method oftransmitting control information in a wireless communication system thatsubstantially obviates one or more of the problems due to limitationsand disadvantages of the related art.

An object of the present invention is to provide a method oftransmitting control information in a wireless communication system, inwhich the wireless communication system operates in CoMP mode.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

Technical Solution

In order to solve the above technical problems, a method of receivingcontrol information in a mobile station which receives downlink datafrom a plurality of cells simultaneously in a wireless communicationsystem comprises receiving downlink control information including thecontrol information on data transmitted from the plurality of cells froma serving base station via a downlink control channel.

Preferably, the mobile station receives the downlink data from theplurality of cells and is able to transmit ACK/NACK for the downlinkdata using a cyclic shift value determined according to a first CCEindex of the downlink control channel and a base sequence of the servingbase station.

Preferably, the method further includes the step of transmitting a CQIof a downlink channel of each of the plurality of cells using a basesequence of the serving base station and a cyclic shift value reservedby the serving base station in advance.

Preferably, the downlink control information includes information on acell having a best downlink channel status among the plurality of cellsand the mobile station is able to receive the downlink data from thecell having the best downlink channel status.

In order to solve the above technical problems, a method of receivingcontrol information of a mobile station operating in a CoMP mode in awireless communication system includes transmitting information on abase station having a best downlink channel status among a plurality ofbase stations coordinated in the CoMP mode of the mobile station usingan index of a precoding matrix and receiving downlink controlinformation from the base station having the best channel status via adownlink control channel.

Preferably, the mobile station receives downlink data from the basestation having the best channel status and is able to transmit ACK/NACKfor the downlink data using a cyclic shift value determined according toa first CCE index of the downlink control channel and a base sequence ofthe base station having the best channel status.

In order to solve the above technical problems, a method of transmittingcontrol information of a serving base station in a wirelesscommunication system includes transmitting downlink control informationincluding the control information on data transmitted from a pluralityof cells to a mobile station receiving downlink data from the pluralityof cells simultaneously via a downlink control channel.

Preferably, the serving base station transmits the downlink data to themobile station and is able to receive ACK/NACK for the downlink datausing a cyclic shift value determined according to a first CCE index ofthe downlink control channel and a base sequence of the serving basestation.

Preferably, the serving base station is able to receive a CQI of adownlink channel of each of the plurality of cells from the mobilestation using a base sequence of the serving base station and a cyclicshift value reserved by the serving base station in advance.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

Advantageous Effects

According to embodiments of the present invention, a serving basestation is enabled to transmit downlink control information to a mobilestation, whereby a method of transmitting control information in awireless communication system operating in CoMP mode is provided.

It is to be understood that the advantages that can be obtained by thepresent invention are not limited to the aforementioned advantages andother advantages which are not mentioned will be apparent from thefollowing description to the person with an ordinary skill in the art towhich the present invention pertains.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a diagram for a configuration of an MIMO communication systemaccording to a related art;

FIG. 2 is a diagram of channels between a receiving antenna i and N_(T)transmitting antennas, respectively;

FIG. 3 is a conceptional diagram for CoMP (coordinated multi-point) ofan intra eNB and an inter eNB according to a related art;

FIG. 4 is a flowchart for a method of receiving control informationaccording to a first embodiment of the present invention;

FIG. 5 is a flowchart for a method of receiving control informationaccording to a second embodiment of the present invention;

FIG. 6 is a flowchart for a method of receiving control informationaccording to a third embodiment of the present invention;

FIG. 7 is a flowchart for a method of receiving control informationaccording to a fourth embodiment of the present invention; and

FIG. 8 is a block diagram for a configuration of a device applicable toa user equipment or base station for performing the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. In the following detailed description of the inventionincludes details to help the full understanding of the presentinvention. Yet, it is apparent to those skilled in the art that thepresent invention can be implemented without these details. Forinstance, although the following descriptions are made in detail on theassumption that a mobile communication system includes 3GPP LTE system,they are applicable to other random mobile communication systems exceptunique features of 3GPP LTE.

Occasionally, to prevent the present invention from getting more vague,structures and/or devices known to the public are skipped or can berepresented as block diagrams centering on the core functions of thestructures and/or devices. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Besides, in the following description, assume that a terminal is acommon name of such a mobile or fixed user stage device as a userequipment (UE), a mobile station (MS) and the like and that a basestation is a common name of such a random node of a network stagecommunicating with a terminal as a node B, eNode B, a base station andthe like.

A base station transmits downlink control information to a mobilestation via a physical downlink control channel (PDCCH). And, the mobilestation transmits uplink control information to the base station via aphysical uplink control channel (PUCCH). The downlink controlinformation and the uplink control information are explained as follows.

First of all, the downlink control information includes controlinformation on data transmitted in downlink or uplink. Therefore, amobile station detects a downlink control channel and then determineswhether there exists data to be transmitted to the mobile station orwhether to transmit data. In general, a downlink control channel istransmitted each subframe. The mobile station activates a randomfunction using a mobile station ID and then determines whether adownlink control channel is transmitted to the mobile station.

A base station generates a downlink control channel by having a basicunit set to a predetermined number of resources in a frequency region.In LTE system, 36 frequency region resources are set to one controlchannel element (hereinafter abbreviated CCE) and control information isthen transmitted. In consideration of a data information sizetransmitted to a mobile station, a channel status, an operational modeand the like, plural CCEs are put together to transmit controlinformation. In the LTE system, it is defined that control informationcan be transmitted by putting 1, 2, 4 or 9 CCEs together.

The downlink control information is interleaved in the frequency regionto be transmitted on a whole downlink band. Since a processingcapability of a mobile station is limited, it is substantially difficultto determine a presence or non-presence of a signal of the mobilestation by discovering all locations of available downlink channels.Therefore, after a location for transmitting control information to themobile station has been designated as a random function using a mobilestation, the mobile station determines a presence or non-presence of adownlink control signal transmitted to itself for the correspondinglocation only.

The downlink control information can be divided into control informationon downlink data and control information on uplink data. The controlinformation on the downlink data includes information on resourceallocation, information on modulation and coding, information on an HARQ(hybrid automatic repeat request) process, a new data indicator,information on a redundancy version, information on power control andthe like. And, if MIMO antenna is supported, the control information onthe downlink data additionally includes information related toprecoding. And, the control information on the downlink data is defineddifferent according to an operational mode.

The control information on uplink data includes information on resourceallocation, hopping information, information on modulation and coding,information on an HARQ process, a new data indicator, power controlinformation, information on a resource of a reference signal fordemodulation, and a channel quality indicator (hereinafter abbreviatedCQI) transmission request information.

And, the uplink control information includes ACK/NACK(acknowledge/non-acknowledge) for the data transmitted in downlink andCQI information indicating a downlink channel status.

The ACK/NACK is transmitted by CDM (code division multiplexing) used ina manner that plural users share a resource of a specific frequencyregion. If it is unable to accommodate a user in a specific frequencyregion, FDM (frequency division multiplexing) for further allocating aresource in a frequency region is additionally used. If the ACK/NACK istransmitted by code division multiplexing, CAZAC sequence is used. Indoing so, a base sequence of a CAZAC sequence is identical in one cell.And, different mobile stations use different cyclic shift values,respectively. The cyclic shift value, which is to be used by the mobilestation, is determined according to a first CCE index of the CCEscarrying the downlink control channel.

A base sequence of the CAZAC sequence used in transmitting the CQI isidentical to the base sequence used in transmitting the ACK/NACK. And, acyclic shift value to be used and a position of a frequency region arereserved in advance.

In the following description, a method of receiving control informationaccording to a first embodiment of the present invention is explainedwith reference to FIG. 4.

FIG. 4 is a flowchart for a method of receiving control informationaccording to a first embodiment of the present invention.

According to a first embodiment of the present invention, a mobilestation receives downlink control information from one of a plurality ofcoordinated base stations. In this case, the base station, whichtransmits downlink control information, is named a serving base station.And, the serving station can be determined after an initial access of amobile station. A plurality of the base stations in CoMP operation sharedata and scheduling information with each other. All the base stationscoordinated in the CoMP mode of the mobile station can transmit thedownlink data to the mobile station or at least one of the base stationscoordinated in the CoMP mode of the mobile station can transmit thedownlink data to the mobile station.

Referring to FIG. 4, a mobile station receives downlink controlinformation from a serving base station [S410].

In this case, the mobile station searches downlink control channels ofthe serving base station only and then determines whether the downlinkcontrol channel for the mobile station only is transmitted. If aplurality of cells among cells coordinated in the CoMP mode of themobile station transmit downlink data to the mobile station, the servingstation transmits downlink control information on the downlink datatransmitted to the mobile station from a plurality of the cells.

The control information transmitted to the mobile station can betransmitted via one downlink control channel or a plurality of downlinkcontrol channels. In particular, if there are two cells that transmitdownlink data to the mobile station, control information on the datatransmitted from one or two cells can be transmitted via one or twodownlink control channels.

The mobile station receives the downlink data from at least one or morecells using the received downlink control channel(s) [S420].

Subsequently, the mobile station transmits uplink control information[S430]. In this case, the uplink control information includes ACK/NACKfor the downlink data, a CQI indicating a channel status in downlink anda scheduling request (hereinafter abbreviated SR).

In case that a plurality of cells transmit downlink data to the mobilestation, control information on the data transmitted from a plurality ofthe cells is transmitted via one control channel. This case is explainedas follows.

First of all, the mobile station uses a base sequence of the servingbase station as a base sequence of CAZAC sequence, determines a cyclicshift value using a first CCE index of the downlink control channeltransmitted by the serving base station, and then transmits ACK/NACK forthe received downlink data. And, a position of a frequency region usedfor the transmission of the ACK/NACK and an orthogonal cover aredetermined according to the first CCE index of the downlink controlchannel transmitted by the serving base station.

The mobile station uses the base sequence of the serving base station asthe base sequence of the CAZAC sequence and then transmits the CQI andthe SR via the position of the frequency region previously determined bythe serving base station using the cyclic shift value previouslyreserved by the serving base station. In doing so, if the downlink dataare received from a plurality of the cells, CQIs of the downlinkchannels of a plurality of the cells, which have transmitted thedownlink data, are transmitted.

In the following description, explained is a case that controlinformation on data transmitted to a mobile station from a plurality ofcells is transmitted via a plurality of downlink control channels.

First of all, in transmitting ACK/NACK, the mobile station uses a basesequence of a serving base station as a base sequence of a CAZACsequence and then determines a cyclic shift value, an orthogonal coverand a frequency region according to a first CCE index of a random one ofa plurality of downlink control channels.

Subsequently, the mobile station uses the base sequence of the servingbase station as the base sequence of the CAZAC sequence and uses thecyclic shift value previously reserved by the serving base station,thereby transmitting a CQI and an SR via the position of the frequencyregion designated by the serving base station in advance.

In the following description, a method of receiving control informationaccording to a second embodiment of the present invention is explainedwith reference to FIG. 5.

FIG. 5 is a flowchart for a method of receiving control informationaccording to a second embodiment of the present invention.

According to a second embodiment of the present invention, a mobilestation receives downlink control information from one of a plurality ofcoordinated base stations. In this case, the base station, whichtransmits downlink control information, is named a serving base station.And, the serving station can be determined after an initial access of amobile station. A plurality of the cells coordinated in CoMP mode of themobile station share data and scheduling information with each other.And, a cell having a best downlink channel status transmits downlinkdata to the mobile station.

Referring to FIG. 5, a mobile station receives downlink controlinformation from a serving base station [S510].

In this case, the downlink control information includes information on acell which transmits the downlink data with a best downlink channelstatus among a plurality of cells coordinated in a CoMP mode of themobile station.

The downlink control information can include a cell ID of the cell thattransmits the downlink data or can indicate a cell that transmits thedownlink data using a precoding matrix.

A case of indicating a downlink data using a precoding matrix isexplained as follows.

First of all, assume that MIMO transmission, in which a plurality ofcells coordinated in the CoMP mode of the mobile station apply precodingcooperatively, is performed. If there are two cells coordinated in theCoMP mode of the mobile station and each of the two cells has twotransmitting antennas, there are total four transmitting antennas. And,it is able to design that cell selection information is included in aprecoding matrix that uses four transmitting antennas.

For instance, when a rank is 1, if such a precoding matrix as {[1 1 00], [1-1 0 0], [1 j 0 0], [1-j 0 0], [0 0 1 1], [0 0 1 1], [0 0 1 j], [00 1-j]} is added, it brings an effect as if information on a cellselected from two cells is transmitted. If a precoding matrixcorresponding to another rank is designed by the same principle, it isable to transmit information related to the selected cell.

Meanwhile, the mobile station receives the downlink data from the cellhaving the best channel status using the received downlink controlchannel(s) [S520].

Subsequently, the mobile station transmits uplink control information[S530]. In this case, the uplink control information includes ACK/NACKfor the downlink data, a CQI indicating a channel status in downlink anda scheduling request (hereinafter abbreviated SR).

The mobile station uses a base sequence of the serving base station as abase sequence of CAZAC sequence, determines a cyclic shift value using afirst CCE index of the downlink control channel transmitted by theserving base station, and then transmits ACK/NACK for the receiveddownlink data. And, a position of a frequency region used for thetransmission of the ACK/NACK and an orthogonal cover are determinedaccording to the first CCE index of the downlink control channeltransmitted by the serving base station.

The mobile station uses the base sequence of the serving base station asthe base sequence of the CAZAC sequence and then transmits the CQI andthe SR via the position of the frequency region previously determined bythe serving base station using the cyclic shift value previouslyreserved by the serving base station.

In the following description, a method of receiving control informationaccording to a third embodiment of the present invention is explainedwith reference to FIG. 6.

FIG. 6 is a flowchart for a method of receiving control informationaccording to a third embodiment of the present invention.

According to a third embodiment of the present invention, a mobilestation receives downlink control information from all or a portion of aplurality of cells coordinated in a CoMP mode of the mobile station. Thecell having transmitted the downlink control information transmitsdownlink data to the mobile station. In doing so, a plurality ofcoordinated base stations share data and control information with eachother.

Referring to FIG. 6, a mobile station receives downlink controlinformation from a plurality of cells [S610].

Each of a plurality of the cells transmitting the downlink data to themobile station transmits downlink control information to the mobilestation.

The mobile station receives the downlink data from a plurality of thecells using a received downlink control channel [S620].

For instance, in case that two cells transmit downlink controlinformation and downlink data to a mobile station, if a first cellallocates a resource of a specific frequency region to the mobilestation, a second cell may not allocate the region to mobile stations ofthe second cell. Yet, if the second cell allocates a resource to themobile station by having the resource avoid being overlapped with theformer resource allocated by the first cell and the first cell does notallocate the corresponding region to mobile stations of the first cell,the mobile station has many resources allocated thereto with thecoordination between the first and second cells and is then able toreceive data. In case of determining that influence of an adjacent cellis not meaningful (e.g., a center of a cell, etc.), the first and secondcells can allocate a resource used by another cell to the mobilestation.

Subsequently, the mobile station transmits uplink control information(S630) In this case, the uplink control information includes ACK/NACKfor the downlink data, a CQI indicating a channel status in downlink anda scheduling request (hereinafter abbreviated SR).

As mentioned in the foregoing description, a base sequence of CAZACsequence used in transmitting ACK/NACK differs for each cell and a usedcyclic shift value is determined according to a first CCE index of CCEscarrying a downlink control channel. A base sequence of CAZAC sequenceused in transmitting CQI differs for each cell as well. And, a cyclicshift value to be used and a position of a frequency region are reservedby a base station in advance.

According to the third embodiment of the present invention, ACK/NACK andCQI can be transmitted in a following manner.

First of all, an ACK/NACK transmitting method is explained. A basesequence of a serving base station among a plurality of base stationshaving transmitted downlink control channels to a mobile station is usedas a base sequence of a CAZAC sequence. And, it is able to transmitACK/NACK using a cyclic shift value, which is determined according to aCCE index of the downlink control channel of the serving base station,an orthogonal cover and a frequency region.

Alternatively, a mobile station is able to transmit ACK/NACK fordownlink data transmitted from each of a plurality of cells using a basesequence of each of a plurality of the cells, a cyclic shift value,which is determined according to a CCE index of a downlink controlchannel of each of a plurality of the cells, an orthogonal cover and afrequency region. In this case, if acknowledgements/non-acknowledgements(ACKs/NACKs) for a plurality of the cells are simultaneouslytransmitted, it may violate a single carrier property.

Secondly, a CQI transmitting method is explained as follows.

In case that CQI information on downlink channels of a plurality ofcells is simultaneously transmitted, a base sequence of a serving basestation in a plurality of cells having transmitted downlink controlchannels to a mobile station is used as a base sequence of a CAZACsequence and it is able to transmit CQI information using a cyclic shiftvalue reserved by the serving base station in advance. In this case, thetransmitted CQI information includes all CQI information of a pluralityof the cells.

Alternatively, a mobile station is able to transmit a CQI of a downlinkchannel of each of a plurality of cells using a base sequence of each ofa plurality of the cells and a cyclic shift value and frequency resourcereserved by each of a plurality of the cells.

In case that CQI information on a downlink channel of each of aplurality of cells is transmitted at a different time, a CQI of adownlink channel of each of a plurality of the cells is transmittedusing a base sequence of each of a plurality of the cells and a cyclicshift value and frequency resource reserved by each of a plurality ofthe cells in advance.

And, the mobile station transmits an SR via the frequency resourcepre-designated using the base sequence of the serving base station andthe cyclic shift value reserved by the serving base station in advance.

In the following description, a method of receiving control informationaccording to a fourth embodiment of the present invention is explainedwith reference to FIG. 7.

FIG. 7 is a flowchart for a method of receiving control informationaccording to a fourth embodiment of the present invention.

According to a fourth embodiment of the present invention, a mobilestation transmits information on a cell having a best channel statusamong a plurality of cells coordinated in a CoMP mode of the mobilestation and then receives downlink control information and downlink datafrom the cell having the best channel status.

Referring to FIG. 7, a mobile station transmits information on a cellhaving a best channel status among a plurality of cells coordinated in aCoMP mode of the mobile station [S710].

In transmitting the information on the cell having the best channel, themobile station transmits a cell ID of the cell having the best channelstatus or the information on the cell having the best channel statususing an index of a precoding matrix.

When MIMO transmission, in which a plurality of cells apply precodingcooperatively, is performed, it is able to indicate a cell having a gooddownlink channel status using an index of a precoding index.

For instance, if there are two coordinated cells and each of the twocells has two transmitting antennas, there are total four transmittingantennas. In this case, it is able to design that cell selectioninformation is included in a precoding matrix that uses fourtransmitting antennas. For example, when a rank is 1, if such aprecoding matrix as {[1 1 0 0], [1-1 0 0], [1 j 0 0], [1-j 0 0], [0 0 11], [0 0 1 1], [0 0 1 j], [0 0 1-j]} is added, it is able to transmitinformation on a selected one of the two cells using an index of theprecoding matrix. If a precoding matrix corresponding to another rank isdesigned by the same principle, it is able to transmit informationrelated to the selected cell.

The mobile station receives downlink control information from the cellhaving the best channel status [S720] and then receives downlink datafrom the corresponding cell [S730].

Subsequently, the mobile station transmits uplink control information[S740]. In this case, the uplink control information includes ACK/NACKfor the downlink data, a CQI indicating a channel status in downlink andan SR.

The mobile station uses a base sequence of the cell having the bestchannel status as a base sequence of a CAZAC sequence, determines acyclic shift value using a CCE index of a downlink control channeltransmitted by the cell having the best channel status, and thentransmits the ACK/NACK for the received downlink data. And, a positionand orthogonal cover of a frequency region used for the transmission ofthe ACK/NACK are determined according to a first CCE index of thedownlink control channel transmitted by the cell having the best channelstatus.

The mobile station uses a base sequence of the cell having the bestchannel status as a base sequence of a CAZAC sequence and then transmitsa CQI and SR via a position of a frequency region pre-designated by thecell having the best channel status using a cyclic shift value reservedby the cell having the best channel status in advance.

FIG. 8 is a block diagram for a configuration of a device applicable toa user equipment or base station for performing the present invention.Referring to FIG. 8, a device 600 includes a processing unit 601, amemory unit 602, an RF (radio frequency) unit 603, a display unit 604and a user interface unit 605. A layer of a physical interface protocolis performed by the processing unit 601. The processing unit 601provides a control plane and a user plane. A function of each layer canbe performed by the processing unit 601. The memory unit 602 iselectrically connected to the processing unit 601. And, an operatingsystem, applications and general files are stored in the memory unit602. If the device 600 is a user equipment, the display unit 604 is ableto display various kinds of informations. And, the display unit 604 canbe implemented using a well-known LCD (liquid crystal display), an OLED(organic light emitting diode) display and the like. The user interfaceunit 605 can be configured by being combined with such a well-known userinterface as a keypad, a touchscreen and the like. The RF unit 603 iselectrically connected to the processing unit 601. The RF unit 603transmits or receives a radio signal.

As mentioned in the foregoing description, the detailed descriptions forthe preferred embodiments of the present invention are provided to beimplemented by those skilled in the art. While the present invention hasbeen described and illustrated herein with reference to the preferredembodiments thereof, it will be apparent to those skilled in the artthat various modifications and variations can be made therein withoutdeparting from the spirit and scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention that come within the scope of the appendedclaims and their equivalents. For instance, the respectiveconfigurations disclosed in the aforesaid embodiments of the presentinvention can be used by those skilled in the art in a manner of beingcombined with one another.

Therefore, the present invention is non-limited by the embodimentsdisclosed herein but intends to give a broadest scope matching theprinciples and new features disclosed herein.

The invention claimed is:
 1. A method of receiving control informationby a mobile station in a wireless communication system, the methodcomprising: receiving a plurality of downlink control channels from aplurality of cells, when the mobile station is configured in acooperation mode in which the plurality of cells provide multi-flowtransmission to the mobile station; receiving a plurality of datachannels from the plurality of cells based on each of the plurality ofdownlink control channels; and transmitting simultaneously ACK/NACKinformation for the plurality of cells through a single uplink controlchannel in accordance with the cooperation mode.
 2. The method of claim1, wherein the ACK/NACK information associated with each of theplurality of data channels is transmitted using a cyclic shift valuedetermined according to a first CCE index of a downlink control channeland a base sequence of a serving cell of the plurality of cells.
 3. Themethod of claim 2, wherein a resource for transmission of the ACK/NACKinformation is determined based on the first CCE index of the downlinkcontrol channel of the serving cell.
 4. The method of claim 1, furthercomprising: transmitting simultaneously channel quality information(CQI) associated with each of the plurality of cells through the singleuplink control channel in accordance with the cooperation mode.
 5. Themethod of claim 1, wherein the plurality of cells operate on a samefrequency.
 6. The method of claim 1, further comprising: detecting theplurality of downlink control channels simultaneously.
 7. A mobilestation for receiving control information in a wireless communicationsystem, the mobile station comprising: a radio frequency (RF) unit; anda processor configured to: receive via the RF unit a plurality ofdownlink control channels from a plurality of cells, when the mobilestation is configured in a cooperation mode in which the plurality ofcells provide multi-flow transmission to the mobile station; receive viathe RF unit a plurality of data channels from the plurality of cellsbased on each of the plurality of downlink control channels; and causethe RF unit to transmit simultaneously ACK/NACK information for theplurality of cells through a single uplink control channel in accordancewith the cooperation mode.
 8. The mobile station of claim 7, wherein theprocessor is further configured to: cause the RF unit to transmit theACK/NACK information associated with each of the plurality of datachannels using a cyclic shift value determined according to a first CCEindex of a downlink control channel and a base sequence of a servingcell of a plurality of cells.
 9. The mobile station of claim 8, whereinthe processor is further configured to: determine a resource fortransmission of the ACK/NACK information based on the first CCE index ofthe downlink control channel of the serving cell.
 10. The mobile stationof claim 7, the processor is further configured to: cause the RF unit totransmit simultaneously channel quality information (CQI) associatedwith each of the plurality of cells through the single uplink controlchannel in accordance with the cooperation mode.
 11. The mobile stationof claim 7, wherein the processor is further configured to detect theplurality of downlink control channels simultaneously.